I know that is not ethic to post challenge like this on this site but there no proper page dedicate for challenge and I write not enough for my profile to be effective thus I post I challenge/request to try to aliment the number of story Ash/Serena because I began to like this shipping very much. Here I will give you a base plot, some things that I would like to read in your fic and some I would prefer not read but otherwise, if you choose to write this, it will be yours.

The right companion

Six years after the League Pokémon of all regions ret up the age to begin a Pokémon quest at 12 year, Cynthia Shirona, after a long journey, challenge The Elite Four of her home Region, Sinnoh. She succeed to conquer the four elite but lose to the Champion who counsel her to study the Pokémon battles from another point of view before reattempt the challenge.

Following this advise Cynthia travel to Kanto region for meet the professor Oak and request a internship but when she arrive she meet a young Ash of 11 year who wish to study Pokémon before starting his Quest to be a Pokémon Master. Observing the potential in Ash, Cynthia decides to mentor him.

A year later, shortly before Ash 12 birthday, Delia receives a phone call from one of her Friend, Grace, a former champion of Rhyhorn Course, her daughter, Serena, wish to travel with Ash. The young man, finding out about the news, is excited to travel with his childhood friend / crush with which he corresponded since his seventh year.

One week before the beginning of his quest Ash save a temperamental Pikachu from a flock of Spearow and nurse him back to health. The Pokémon and the human befriend and Ash decides that Pikachu will be his starter.

Cynthia, after one year tutoring Ash, chooses to travel with him for a bit, to continue to mentor him and to observe his progress. The day after his registration as a trainer, Ash with Cynthia waits at the airport by Bourg-Palette, the arrival of Serena.

With his mentor and his true love (even if he doesn't know), Ash may begin his quest to the top.

This is the base plot and for other indications:

-Ash mentored by Cynthia is more mature and less reckless but he is always a poke-enthusiast, eager to test every domain relied to Pokémon

-Brock follow the general plot of the Anime but chose his profession of doctor Pokémon much earlier, like in the anime he slit up with the group at the begin of the Orange Island and return for the league johto after studying under one year under doctor Nina Oak, the grand-daughter of professor Oak. After he rest with Ash and Serena even during Unova and Kalos

-Serena, like in the anime, don't know her future purpose but talking with Brock, she find a passion in breeding Pokémon and, when traveling in Hoenn, a hobby in Contest.

-After the victory of Ash in the Orange League, Cynthia decide to return in Sinnoh to try again the Elite Four, before her depart she said to Ash that she wait for his Challenge.

-After the Orange League, Ash and Serena travel To Hoenn before Johto, Professor Birch will offer to Ash a temperamental Torchic who love battle. During the journey, the couple meets another couple, Brendan (perso from R,S,E) and May who will be the rival for Ash and Serena in the League and Contest.

-The Crime Syndicate follow the pattern of a mix between the game, the anime and the manga. The Rocket Trio is not present beyond the Indigo League.

-After Battle Frontier, Serena obtain a diploma in breeding thus, with the high grade of Ash, they have the permission to have more than six Pokémon with them.

-In Sinnoh, the group travel with a young Dawn and Luka (perso from DP and Platine) and mentor them in the marvel of Pokémon.

-Ash improve in Each League for finally win in the Sinnoh League but lose a first time to Cynthia, after he won the Unova and Kalos League but also lose to either one member of the Elite four or the Champion.

-The Fic end with the Victory of Ash face to Cynthia.